1. Field of the Invention
This invention is directed to systems and methods for multipass fluid ejection systems.
2. Description of the Related Art
The popularity of computer printers has fueled development of more efficient and quiet printers that generate high quality images in both black/white and color formats.
Multipass liquid inkjet printers form images by sweeping a print head apparatus over a substrate and ejecting a series of liquid ink droplets onto the receiving substrate and advancing the substrate as necessary. The process by which the print head apparatus is swept across the receiving substrate, the ejection of a series of liquid ink droplets, and the advancement of the receiving substrate comprise a multiple pass (or multipass) routine.
Meeting the increasing demand for speed and higher quality, photo-like, full color imaging has created the need for a system that operates within the entire spectrum. In this regard, a system should be capable of transferring a large amount of liquid ink onto a receiving substrate. By placing a large amount of liquid ink onto a receiving substrate, especially when contrasting colored ink droplets are placed adjacent to each other, may result in cockling of the paper, beading, undesirable color coalescence or other observable artifacts.
Although inkjet printers may initially produce very high quality images, the droplet size and placement accuracy may worsen with time due to mechanical and electrical fatigue factors associated with the print head nozzles of such printers. Furthermore, such nozzle fatigue factors generally manifest in pattern-like printing errors that are quite noticeable to a user, particularly when the printing mode is a single-pass printing mode.
Accordingly, as shown in FIGS. 1, 2, 3 and 4A-4C, in the prior art systems, which printed a particular pixel element in a non-randomized, repeated sequence, noticeable pattern-like printing errors commonly occur. FIG. 1 illustrates one conventional fluid ejection apparatus 10 usable for depositing fluid droplets on a receiving substrate. As shown in FIG. 1, the conventional fluid ejection apparatus includes a carriage 12 movable along the direction A upon one or more guide rails 14 and 16. The carriage 12 may include a single fluid cartridge 26 or multiple fluid ink cartridges 26B, 26M, 26C and 26Y, containing one or more different types of fluids.
FIG. 2 illustrates a conventional fluid head ejection cartridge. As shown in FIG. 2, droplets of the fluid are ejected from nozzles 32 which are usually linearly arranged in a nozzle face of the fluid cartridge 26. It is well known in the art that the quality of the placement of the fluid drops on the receiving substrate is affected by the ability of the receiving substrate to absorb the fluid and/or the performance of nozzles in applying the fluid to the receiving substrate.
In generating a pattern of fluid drops on the receiving substrate, the fluid is desirably applied to only those areas on the receiving substrate corresponding to the pattern being reproduced, and not leaving any areas, which the fluid is to be applied, without the fluid. It is well known, when the fluid is one or more differently colored inks, to deposit the ink onto the receiving substrate such that the drops of ink, corresponding to one or more colors or one or more color combinations, overlap.
It is well known in the art to eject the fluid drops forming the desired pattern one swath at a time by passing the fluid ejection cartridge over the same area the receiving substrate multiple times. A swath is typically defined as the width of the array of nozzles 32 in the direction orthogonal to the fast scan direction A, i.e., the process direction B. During each pass over a particular swath, drops of the fluid are ejected only for certain pattern portions of the pattern. It is also known in the art to advance the receiving substrate 28 relative to the fluid cartridge 26 by a partial swath in the process direction B between passes when printing a single swath of the desired pattern.
FIG. 3 illustrates a conventional technique for ejecting fluid onto a receiving substrate. As shown in FIG. 3, the conventional technique for ejecting fluid onto a receiving substrate may be used to avoid uninked portions occurring between the ink drops. More specifically, the conventional technique for ejecting fluid onto a receiving substrate may be used, for example, to avoid uninked white portions, if the recording substrate is white, occurring between the ink drops.
However, overlapping fluid drops is known to cause beading. Beading is an undesirable condition that occurs when overlapping drops of adjacent pattern areas, such as pixels in an image, are deposited when the fluid is still free to flow. When adjacent fluid drops spread over the surface of the receiving substrate, fluid from one drop will overlap and form into the portion occupied by the fluid of another drop. As a result, the density of the pattern image may appear non-uniform because of the differing areas of high and low amounts of fluid that result from the beading.
Conventionally, as shown in FIGS. 4A-4C, the fluid drops are applied in an alternate checkerboard to avoid beading on the receiving substrate. For example, if two passes are made, xc2xd of the fluid drops are printed in a checkerboard pattern on each pass. That is, the checkerboard pattern is overlaid on the pattern of fluid drops to divide the pattern portions into two sets. Fluid drops, corresponding to the first set of portions of the pattern portions, are ejected on the first pass, as shown in FIG. 4A. Then, the remaining pattern portions, corresponding to the second set of portions of the pattern portions, receive fluid drops, as shown in FIG. 4B.
Then, as shown in FIG. 4C, for a third pass of the two-pass mode, the pattern repeats. Specifically, the third pass begins with the checkerboard pattern overlaid on the pattern of fluid drops for the second swath of image data and the data is divided into another set of two portions. The fluid drops, corresponding to the first set of portions, are ejected on the first pass of the second swath, as shown in FIG. 4C. However, problems may still arise that affect the pattern quality of the ejected fluid drops, if there are failures in the performance of the nozzles of the fluid ejection cartridges 26.
To improve print quality, multiple passes are typically used in ink jet printing. In a two-pass mode, pixels corresponding to one color of a checkerboard pattern are printed on the first pass, and the remaining pixels on the second pass. For example, U.S. Pat. No. 4,748,453 to Lin et al., incorporated herein in its entirety, depicts an example of a two-pass mode system in FIGS. 1-4.
In operation, a multiple pass mode system of N passes prints a fraction 1/N of the pixels on each pass. In this fraction, the deposited ink has time to dry between passes, and is less likely to cause mottling or many of the other undesirable artifacts common to draft mode ink jet printing. Commonly, the print head is advanced a partial swath between passes. This allows another nozzle or series of nozzles to fire and eject ink resulting in a partial printed swath. Because a plurality of nozzles are used to print on a given scanline, defects in any one nozzle are less visible. As commonly practiced in the art, in an N-pass mode, the pixels printed on a given pass are specified by one of a fixed set of regular patterns.
This invention provides systems and methods that eject fluid in patterns that improve the quality of a printed image.
This invention separately provides systems and methods that eject fluid for a swath in a random or pseudo-random manner relative to other swaths.
In various exemplary embodiments of the systems and methods according to this invention, image data is input and associated with corresponding pixel elements for a particular swath of print data in an N-pass mode multipass system. A plurality of random numbers Q are generated within a particular range R of possible numbers. Each random number is associated with one or more pixels to be printed in the current swath for all of the passes used to completely print the image data for those pixels.
As a first pass for a particular set of pixels is begun, a start state of a random number generator is saved. Before each subsequent pass for that particular set of pixels is begun, the state of the random number generator is reset to the saved start state. As a result, the same random numbers will be generated for that particular set of pixels for each of the N passes used to completely print that set of pixels. The random number associated with each set of one or more pixels controls which pixels of that set are enabled in each pass, i.e., which pass a particular pixel will be printed in.
These and other features and advantages of the invention are described in or apparent from the following detailed description of the preferred embodiment.